Pulse stretcher



June 25, 1957 Input W. F. STEAGALL PULSE STRETCHER Filed Sept. 24, 1954 l/ IO INVENTOR WILL/A M- F STEA GALL BY WW ATTORNEY United States atent PULSE STRETCI-IER William F. Steagall, Merchantville, N. 3., assignor to Sperry Rand Corporation, a corporation of Delaware Application September 24, 1954, Serial No. 458,039

Claims. (Cl. 307-88) This invention relates to pulse stretching devices and in particular to such a device having a magnetic core. The purpose of a pulse stretcher is to provide an output pulse of considerably longer duration than the input pulse which actuates the device.

It is an object of the invention to provide a pulse stretcher for producing output pulses of accurately timed predetermined length. Related devices are known in the prior art but they are complicated, of large size, and lack the requisite reliability of performance as they include elements such as vacuum tubes that are likely to burn out.

It is a primary object of this invention to provide a pulse stretcher which overcomes these disadvantages in the prior art.

Another object of the invention is to provide a pulse stretcher that is extremely simple in construction, has fewer parts than those of the prior art and is easily assembled.

An additional object of the invention is to provide a pulse stretcher that is reliable, accurate in operation and of long life.

Still another object of the invention is to provide a pulse stretcher which has only two diodes or rectifiers.

It is an additional object of the invention to provide a pulse stretcher that employs only one magnetic core.

A further object of the invention is to provide a pulse stretcher that is very small in size.

Another object of the invention is to provide a pulse stretcher that may be conveniently used in computer circuits employing magnetic amplifiers.

It will be understood that the term diode is used herein in a generic sense and includes rectifiers of all kinds whether vacuum tubes, crystals, metals, chemicals or other materials and construction providing a rectifying action.

The invention employs the combination of an inductor, a transformer, a diode, and an output resistor. The transformer and diode are so arranged that the inductor is effectively isolated from the output resistor, during the time that the field in the inductor is being built up,

and efiectively shunted across the output resistor during the time that the field of the inductor is collapsing. As

a result, an input pulse can build up the field around the inductor rapidly, but when the input current ceases and the field around the inductor begins to collapse, the collapsing action is retarded because during this period the output resistor is in effect shunted across the inductor and therefore the output current is stretched or prolonged as compared to the period of the input current. Further details will appear as this description proceeds.

In the drawings:

Figure 1 is a schematic diagram of a preferred form of the invention.

Figure 2 is an idealized hysteresis loop for the core material used in the device of Figure l.

The device of Figure 1 has an input 10 for feeding parallel with the inductor applies.

current through. rectifier 11 to coil 13 of the magnetic core C. An inductor 12 is shunted across the core 13. A secondary winding 14 on core C is connected through rectifier 15 to the load resistor 16 and to an output 17. The device is supplied at input 10 with a square wave pulse of a waveform such as W. Preferably there is a steady negative potential on the input, and an input pulse drives the input terminal 10 positive. The core C of the magnetic amplifier may be made of a variety of materials, among which are the various types of ferrites and the various magnetic tapes, including Othonik and 4-79 Moly-Permalloy. These materials may have different heat treatments to give them difierent properties. The magnetic material employed in the core should preferably, though not necessarily, have a substantially rectangular hysteresis loop such as shown in Figure 2. Cores of this character are now well known in the art. In addition to the wide variety of materials available, the core C may be constructed in a number of geometries including both closed and open paths; for example, cupshaped, strips, and toroidal-shaped cores are possible.

Assuming the device to be in its idle condition, at which time the core is at point 24 on the hysteresis loop representing its negative value of residual magnetism, the

r first pulse W will flow into input 10, through rectifier 11,

and through the inductor 12 and the primary winding 13 in parallel. This current flow will cause a field to be established about the inductor l2 and the core will be driven from negative point 24 on its hysteresis loop to near positive saturation. At the conclusion of the pulse the core will return to its positive residual magnetism point 21. During the application of this pulse, no current will flow in the load circuit because the rectifier 15 is connected in the direction to prevent such current flow.

As soon as the pulse W ceases the field about inductor 12 will begin to collapse and will cause current to flow through coil 13 in the opposite direction from the flow of current due to the pulse W. Consequently, current is induced in coil 14 and will flow through the rectifier 15 and the load 16 causing a pulse to appear at the output 17. In this case the inductor 12 is in eifect in parallel with the resistor 16 and consequently the usual relationship governing the time of collapse of a field in an inductor when there is means having impedance in According to this formula, the time required for field collapse varies inversely with the value of the shunting impedance. Consequently, the time period of the output pulse will be inversely dependent upon the value of resistance of resistor 16. If this resistor has low resistance, the relative length of the output pulse may be very long as compared to the duration of the input pulse. During the time that the field of inductor 12 is collapsing, the inductive reaction will produce a voltage which will tend to drive the core from point 21 on the hysteresis loop through point 22 toward negative saturation 23, and when the field has entirely collapsed the core will have returned to its residual flux density point 24. The device will then be ready to receive and stretch the next pulse fed into input 10.

On the drawing conventional symbols such as l-BS are employed, in addition to reference numbers such as 219. Positive and negative saturation are represented by +BS and BS respectively. Positive and negative remanence points 21 and 24 respectively have conventional symbols +BR and BR respectively. Positive and negative values of magnetizing force where the flux density is zero are designated by +HC and HC respectively in addition to reference numbers 25 and 22 respectively.

The invention may be described in the following way. Assume that the current produced in coil 13 by an input pulse produces a magnetomotive force H in a positive direction in Figure 2. Then when an input pulse is applied at point 10, the core will be driven to saturation point 20 and a current will be produced in inductor 12 which flows in the direction from A to B, this being the direction of the voltage drop. During the application of the input pulse W, the diode 15 prevents current from flowing in the winding 14. At the end of the input pulse W, the field in inductor 12 begins to collapse and produces a voltage drop from B to A which causes current to flow in coil 13 in such a direction as to produce a negative magnetomotive force and to flip the core to negative saturation point 23, and the inductive reactance of coil 12 is in effect shunted across the resistor 16. According to this invention, when it is desired that the output pulse be longer than the input pulse the circuit values are so chosen that the time required for the input pulse W to flip the core from point 24, through point 25 to positive saturation point 20, is much less than the time required for the inductive reaction of industor 12 to flip the core C back from point 21, to negative saturation point 23.

It is clear that essentially the device of the present invention produces an output pulse delayed in time from the input pulse, and ordinarily the output pulse has greater duration that the input pulse. However, the values of the several circuit components may be so selected, if desired, that the output pulse is the same length as, or even shorter than, the input pulse.

While I have shown only one form of my invention, various modifications may be made without departing from the broadest aspects of the invention. Therefore, I am defining the scope of my invention in the appended claims in which generic terms are employed to include those equivalent structures which fall within the spirit of the invention.

Having thus described my invention, I claim:

1. A pulse stretching device comprising in combination an input terminal, a core of magnetic material, first and second windings on said core, the second winding having an output rectifier and means having impedance connected thereacross in series with each other and an output terminal therebetween, the junction of said means and said second winding being connected to ground, an inductor connected across said first Winding and having terminal junctions, an input rectifier, one of said terminal junctions being grounded, the other terminal junction being connected to said input terminal through said input rectifier.

2. The combination set forth in claim 1 in which the forward resistance of said input rectifier, the number of turns on said first winding, the number of turns on said second winding, the forward resistance of said output rectifier, and the resistance of said means are so related that output pulses have longer duration than input pulses.

3. A pulse stretching device comprising in combination a magnetic core, Winding means including an input and an output, said core having a substantially quadrilateral hysteresis loop and circuit means connected to said input and said output for causing an input pulse to flip said core from minus remanence to plus saturation on the hysteresis loop and for thereafter flipping the core back to minus saturation with the time required to flip the core back to minus saturation being longer than that required to flip it to plus saturation, whereby to cause the duration of an output pulse produced at said output to be greater than the duration of a pulse applied to said input and to cause the output pulse to be delayed with respect to said input pulse.

4. In combination in a pulse stretching device, a core of magnetic material, a flux producing coil thereon, input means for feeding the flux producing means, a flux control coil on the core, said core having a substantially quadrilateral characteristic hysteresis loop, means having impedance connected to said flux control coil, and circuit means for effectively shunting said last-named means across said flux producing coil during the portion of the operation cycle of the device when it is producing an output, whereby to cause the time elapse required for flipping the core from minus remanence to plus saturation on said loop is much less than the time consumed by the device in flipping the core back to minus saturation.

5. In combination in a magnetic delay flop, a core of magnetic material having a first winding thereon with an input having a rectifier, a second winding thereon with an output having a rectifier and impedance means in series and circuit means connected to said first winding for flipping said core on its hysteresis loop, said core comprising ferromagnetic material the time constant of which for flipping said core from one remanent point to another on said loop is a function of the applied voltage, the lastnamed means including means whereby the time required for an input pulse to flip the core is less than the time required for the core to be flipped back to its original state after the input pulse ceases.

6. The combination set forth in claim 5, said circuit means comprising an inductor, and said input rectifier having a high forward resistance.

7. In combination in a magnetic delay flop, a core of magnetic material having a substantially rectangular characteristic hysteresis loop, a first flux producing means associated with said core, an input connected to said first flux producing means, an output Winding associated with the magnetic field to be produced in said core, an output circuit connected to said output winding, said core comprising ferromagnetic material the time constant of which for flipping said core from one remanent point to another on said loop is a function of the applied voltage, and circuit means for automatically varying the eflective voltage applied to flip said core from a first value during one excursion on said loop to a second value during a successive excursion on said loop.

8. In combination, in a magnetic delay flop, a core of magnetic material having a substantially rectangular characteristics hysteresis loop, a first winding on said core having an input circuit, a second winding on said core having an output circuit, said core comprising ferromagnetic material the time constant of which for flipping said core from one remanent point to another on said loop is a function of the applied driving voltage, and circuit means for flipping the core in one direction in response to an input pulse and for storing energy during that pulse and for utilizing the stored energy to flip the core back to its original state after the input pulse ceases, the lastnamed means including means which reduces the effective flipping voltage during the return flippingoperation so that the flux density in the core during the latter operation decays over a longer time period than the period of the input pulse.

9. A pulse delay device comprising in combination a magnetic core, winding means including an input and an output, said core having a substantially quadrilateral hysteresis loop and circuit 'means connected to said input and said output for causing an input pulse to flip said core from minus remanence to plus saturation on the hysteresis loop and for thereafter fliping the core back to minus saturation with the time required to flip the core back to minus saturation being shorter than that required to flip it to plus saturation, whereby to cause the duration of an output pulse produced at said output to be less than the duration of a pulse applied to said input and to cause the output pulse to be delayed with respect to said input pulse.

10. In combination, in a magnetic delay flop,'a core, a first winding on said core having an input circuit, a second winding on said core having an output circuit, said core comprising magnetic material the time constant of which for flipping said core from one remanent point to another on said loop is a function of the applied driving 2,797,339 5 6 voltage, and circuit means for flipping the core in one curing the latter operation decays over a time period direction in response to an input pulse and for storing which may be controlled with respect to the period of the energy during that pulse and for utilizing the stored eninput pulse. ergy to flip the core back to its original state after the input pulse ceases, the last-named means including a 1'e- 5 I References Cited in the file of this Pawnt actor shunted across said first winding and means for UNITED STATES PATENTS controlling the eflective flipping voltage during the return 2 436 395 Manley et a1 Feb 24 1948 flipping operation so that the flux density in the core 

